Families on way to injured Qantas pilots

The families of two Australian pilots critically injured in a vintage plane crash are en route to South Africa to be by the pair's side.

Training captain Douglas Haywood and recently retired captain Ross Kelly, both from NSW, were among 19 people aboard the plane that crashed shortly after take-off in Pretoria on Wednesday afternoon (Thursday AEST).

Mr Kelly's wife, Lyndall, was also aboard the stricken flight and is in a stable condition.

It's understood their families are on their way to South Africa, where the men are clinging to life.

The Historical Aircraft Restoration Society, which Mr Haywood and Mr Kelly are members of, said it was "saddened" by the crash.

"Our thoughts go out to not only our members' families but all those involved in South Africa," HARS president Bob De La Hunty said in a statement on Friday.

A South African flight engineer on board the 64-year-old plane and a factory worker were killed in the crash.

The Convair 340 aircraft crashed into a factory near Pretoria's Wonderboom Airport.